Method and eNodeB for forwarding downlink and uplink packets based on S1 handover

ABSTRACT

A method for forwarding downlink packets based on S1 handover is disclosed. The method includes: numbering a packet not processed by using PDCP according to a message that comprises PDCP Serial Number (SN) information if downlink packets to be forwarded include the packet not processed by using PDCP; and sending the downlink packets to the UE according to the PDCP SN corresponding to the packet included in the downlink packets. A method for forwarding uplink packets based on S1 handover is disclosed. The method includes: receiving state report information of the packet sent by the target eNodeB; and sending the packet according to the state report information of the packet. Another method for forwarding downlink packets based on S1 handover and an eNodeB are disclosed. Through the embodiments of the present disclosure, the packets are forwarded without loss in the case of S1 handover.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/732,807, filed on Mar. 26, 2010, which is a continuation ofInternational Application No. PCT/CN2008/072570, filed on Sep. 27, 2008.The International Application claims priority to Chinese PatentApplication No. 200710175412.9, filed on Sep. 29, 2007. Theafore-mentioned patent applications are hereby incorporated by referencein their entireties.

FIELD

The present disclosure relates to the radio communications field, and inparticular, to a method for forwarding downlink and uplink packets basedon S1 handover, and to an evolved NodeB (eNodeB).

BACKGROUND

The Long Term Evolution (LTE) system is in a flattened Radio AccessNetwork (RAN) structure, and requires no Radio Network Controller (RNC).FIG. 1 shows a structure of an LTE system. As shown in FIG. 1, the LTERAN includes an eNodeB and an Evolved Packet Core (EPC). The eNodeBevolves from the NodeB and the RNC in the R6 stage, and differenteNodeB's are interconnected through an X2 interface in the mesh mode.The interface between the eNodeB and the EPC is called an S1 interface.An EPC includes a Mobility Management Entity (MME) and a SystemArchitecture Evolution (SAE) GateWay (SGW). As a control plane part, theMME is responsible for the control plane mobility management, includinguser context and mobility state management, and allocation of aTemporary Mobile Subscriber Identifier (TMSI). As a user plane part, theSGW is responsible for initiating paging for the downlink data in theidle state, and managing and storing the Internet Protocol (IP) bearerparameters and intra-network routing information, and so on. The MME isconnected with the SGW in a mesh mode. That is, one MME controlsmultiple SGWs. The S1 interface supports many-to-many connectionrelationships between the EPC and the eNodeB.

FIG. 2 shows a user-plane protocol stack of an LTE system specific tothe LTE structure shown in FIG. 1. Generally, all functions of the RNCin the existing network are located to the eNodeB so that the eNodeB hasall radio interface protocol stacks. As shown in FIG. 2, the user-planeprotocol stack of the evolved architecture of the layer-2 node includesa User Equipment (UE) user-plane protocol stack, an eNodeB user-planestack protocol, and an SGW user-plane protocol stack. The UEcommunicates with the eNodeB through a Uu interface, and the eNodeBcommunicates with the SGW through an S1 interface.

The SGW user-plane protocol stack includes: a GPRS TunnelingProtocol-User plane (GTP-U) layer, a User Datagram Protocol/InternetProtocol (UDP/IP) layer, an L2 layer, and an L1 layer.

The eNodeB user protocol stack includes a radio interface protocol stackand an S1 interface protocol stack. The radio interface protocol stackincludes: a Packet Data Convergence Protocol (PDCP) layer, a Radio LinkControl (RLC) layer, a Media Access Control (MAC) layer, and an L1layer. The S1 interface protocol stack includes: a GTP-U layer, a UDP/IPlayer, an L2 layer, and an L1 layer.

The UE user-plane protocol stack includes: a PDCP layer, an RLC layer, aMAC layer, and an L1 layer.

The L2 layer refers to layer 2 in the layered protocol, namely, the datalink layer, which includes frame relay, Asynchronous Transfer Mode(ATM), or a radio data link layer. The L1 mentioned above refers tolayer 1 in the layered protocol, namely, the physical layer, whichincludes E1, fiber, and microwave transport.

In the S1 handover process in an LTE system, in order to reduce packetloss, the packet forwarding method based on S1 handover is generallyapplied. However, in the process of forwarding the data, the targeteNodeB is unable to ensure the data forwarding of the target eNodeB tobe orderly, and is hence unable to ensure lossless migration of packets.

SUMMARY

The first aspect of the present disclosure is to provide a method forforwarding downlink packets based on S1 handover, to prevent or reduceloss of downlink packets in the S1 handover, and thus to accomplishforwarding of downlink packets without loss.

The second aspect of the present disclosure is to provide a method forforwarding uplink packets based on S1 handover, to prevent or reduceloss of uplink packets in the S1 handover, and thus to accomplishforwarding of uplink packets without loss.

In order to fulfill the first aspect of the present disclosure, a methodfor forwarding downlink packets based on S1 handover is disclosed in anembodiment of the present disclosure. The method includes: numbering apacket not processed by using PDCP according to a message that carriesPDCP Serial Number (SN) information if downlink packets to be forwardedinclude the packet not processed by using PDCP; and sending the downlinkpackets to a UE according to the PDCNs of packages included in thedownlink packets.

In order to fulfill the first aspect of the present disclosure, anothermethod for forwarding downlink packets based on S1 handover is disclosedin an embodiment of the present disclosure. The method includes:performing PDCP SN numbering for a packet delivered by the target SGW byusing PDCP SN of a special packet as an initial PDCP SN when thedownlink packets to be transmitted include the packet delivered by thetarget SGW, where the PDCP SN of the special packet is obtained afterthe source eNodeB numbers the special packet, and the special packet isobtained by the source eNodeB when the source SGW stops sending packets;and forwarding the downlink packets to a UE according to the PDCNs ofpackages included in the downlink packets.

In the foregoing methods for forwarding downlink packets based on S1handover, the packet not processed by using PDCP is numbered accordingto the message that carries PDCP SN information of the packet, or thepacket delivered by the target SGW is numbered according to the PDCP SNof the special packet. Therefore, the UE can receive downlink packetssequentially in the case of S1 handover, and the downlink packets can beforwarded without loss.

In order to fulfill the second aspect of the present disclosure, amethod for forwarding uplink packets based on S1 handover is disclosedin an embodiment of the present disclosure. The method includes:receiving state report information of a packet sent by a target eNodeB;and sending the packet according to the state report information of thepacket.

In the foregoing method for forwarding uplink packets based on S1handover, the target eNodeB sends the packet state report information tothe UE, thus ensuring that the UE sends the packet according to thepacket state report information in the case of S1 handover, andaccomplishing forwarding of the uplink packets without loss.

An eNodeB is disclosed in an embodiment of the present disclosure. Whenthe eNodeB serves as a target eNodeB, the eNodeB includes: a receivingmodule, adapted to receive a message that includes PDCP SN information;and a sorting module, connected with the receiving module and adapted toperform PDCP SN numbering for a packet according to the message.

A communication system is disclosed in an embodiment of the presentdisclosure. When the communication system includes the eNodeB and theeNodeB serves as a target eNodeB, the eNodeB includes: a receivingmodule, adapted to receive a message that includes PDCP SN information;and a sorting module, connected with the receiving module and adapted toperform PDCP SN numbering for a packet according to the message.

Through a receiving module and a sorting module, the foregoing eNodeBperforms PDCP SN numbering for packets and ensures forwarding of thepackets without loss.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structure of an LTE system;

FIG. 2 shows a user-plane protocol stack of an LTE system;

FIG. 3 is a flowchart based on S1 handover;

FIG. 4 is a flowchart of a method for forwarding downlink packets basedon S1 handover in the third embodiment of the present disclosure;

FIG. 5 is a flowchart of a method for forwarding downlink packets basedon S1 handover in the fourth embodiment of the present disclosure;

FIG. 6 is a flowchart of a method for forwarding downlink packets basedon S1 handover in the fifth embodiment of the present disclosure;

FIG. 7 is a flowchart of a method for forwarding downlink packets basedon S1 handover in the sixth embodiment of the present disclosure;

FIG. 8 is a flowchart of a method for forwarding uplink packets based onS1 handover in the seventh embodiment of the present disclosure;

FIG. 9 is a flowchart of a method for forwarding uplink packets based onS1 handover in the eighth embodiment of the present disclosure;

FIG. 10 is a flowchart of a method for forwarding uplink packets basedon S1 handover in the ninth embodiment of the present disclosure; and

FIG. 11 shows a structure of an eNodeB in an embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure is detailed below by reference to theaccompanying drawings and exemplary embodiments.

In the embodiments of the present disclosure, in order to ensurelossless migration of packets, it is necessary to transfer the packetsunconfirmed and buffered in the source eNodeB and the packets notprocessed in time. For downlink packets, the packets received by thetarget eNodeB may be forwarded from the source eNodeB, or delivered fromthe target SGW. The UE receives packets sequentially according to PDCPSNs. Therefore, the target eNodeB needs to assign a PDCP SN to eachreceived packet. In this way, packet loss is avoided or reduced, andlossless migration of the downlink packets is ensured. For uplinkpackets, the target eNodeB knows which packets from the source eNodeBfail to be received, and instructs the UE to retransmit such packets,thus ensuring lossless transfer of the uplink packets.

FIG. 3 is a flowchart based on S1 handover. The flow includes thefollowing steps:

Step 1: According to the handover algorithm, the source eNodeB decidesto trigger handover through an S1 interface.

Step 2: The source eNodeB sends a Relocation Request message to a sourceMME.

Step 3: The source MME selects a target MME to which a ForwardRelocation Request message is sent.

Step 4: The target MME checks whether the current target SGW cancontinue to serve the UE. If the current target SGW can continue toserve the UE, the process proceeds to step 5; if the current target SGWcannot continue to serve the UE, the target MME selects a new target SGWwhich forwards the packet indirectly. That is, the target SGW of thecore network is relocated. Step 4a and step 4b are performed.

Step 4a: The target MME sends a Create Bearer Request message to the newtarget SGW.

Step 4b: The new target SGW sends a Create Bearer Response message tothe target MME.

Step 5: The target MME sends the Relocation Request message to thetarget eNodeB, and receives a Relocation Response from the eNodeB.Specifically, step 5a: the target MME sends a Relocation Request messageto the target eNodeB; and step 5b: the target eNodeB generates a contextwhich includes bearer information and security context information, andsends a Relocation Response to the target MME.

Step 7: The target MME sends the Relocation Response to the source MME.If the target SGW of the core network is relocated, the following step 6occurs between step 5 and step 7:

Step 6: The target MME notifies the new target SGW of the relevantparameter information. Specifically, step 6 includes:

Step 6a: The target MME sends an Update Bearer Request message to thetarget SGW. The message notifies the new target SGW of the relevantparameter information.

Step 6b: The new target SGW sends an Update Bearer Response message tothe target MME.

If the source SGW of the core network is relocated, the following step 8occurs after step 7.

Step 8: The source MME updates the tunnel information of the source SGW.Specifically, step 8 includes:

Step 8a: The source MME sends an Update Bearer Request message to thesource SGW.

Step 8b: The source SGW sends an Update Bearer Response message to thesource MME.

Step 9: The source MME sends a Relocation Command message to the sourceeNodeB.

Step 10: The source eNodeB sends a Handover Command message to the UE.

Step 11: After the UE is synchronized to the target cell successfully,the UE sends a Handover Confirm message to the target eNodeB. The targeteNodeB sends downlink data forwarded by the source eNodeB to the UE, andthe UE may send uplink data to the target SGW.

Step 12: The target eNodeB sends a Relocation Complete message to thetarget MME.

Step 13: The target MME sends a Forward Relocation Complete message tothe source MME, and receives a Forward Relocation Complete Acknowledgemessage from the source MME. Specifically, step 13 includes:

Step 13a: The target MME sends a Forward Relocation Complete message tothe source MME.

Step 13b: The source MME sends a Forward Relocation Complete Acknowledgemessage to the target MME.

Step 14: The target MME sends an Update Bearer Request message to thetarget SGW.

Step 16: The target SGW sends an Update Bearer Response message to thetarget MME.

If the new target SGW is applied, it indicates that the target SGW isrelocated, and the following step 15 occurs between step 14 and step 16:

Step 15: The new target SGW notifies the Packet Data Network Gate Way(PDN GW) of the new tunnel and address. Specifically, step 15a: The newtarget SGW sends an Update Bearer Request message to the PDN GW; andstep 15b: The new target SGW sends an Update Bearer Response message tothe target MME.

Step 17: The source MME receives the Forward Relocation Completemessage, and sends a Release Resource message to the source eNodeB. Thesource eNodeB releases all resources.

If the source SGW of the core network is relocated, the following step18 occurs:

Step 18: The source MME sends a Delete Bearer Request message to thesource SGW. Specifically, step 18a: The source MME sends a Delete BearerRequest message to the source SGW; and step 18b: The source SGW sends aDelete Bearer Response message to the source MME.

In the embodiments of the present disclosure, the downlink packetsreceived by the target eNodeB include the packets forwarded by thesource eNodeB and the packets delivered by the target SGW. The packetsforwarded by the source eNodeB include the packets processed through thePDCP and the packets not processed through the PDCP. In the packetsforwarded by the source eNodeB, each packet processed through the PDCPcarries a PDCP SN. The packets not processed through the PDCP carry noPDCP SN; and the packets delivered by the target SGW carry no PDCP SN.It is assumed that the packets processed through the PDCP in the sourceeNodeB are category-1 packets; the packets not processed through thePDCP in the source eNodeB are category-2 packets; and the packetsdelivered by the target SGW are category-3 packets.

It is possible that all the category-1 packets of the source eNodeB aresent to the UE before handover. At the beginning of the handover, thesource eNodeB receives responses to only some category-1 packets fromthe UE. The responses indicate that the UE has received such category-1packets. Therefore, in order to save forwarding resources, suchcategory-1 packets are not forwarded, and only the category-1 packets towhich the UE makes no response are forwarded.

After the target eNodeB receives category-1 packets, because category-1packets carry PDCP SNs, they carry the old PDCP SNs and are sent to theUE; if the received packets are category-2 packets and/or category-3packets, because such packets carry no PDCP SN, the target eNodeB needsto assign a PDCP SN to each packet before sending such packets to theUE. In this way, it is ensured that the UE receives the packetssequentially according to the PDCP SN.

The following embodiments 1-6 of the method for forwarding downlinkpackets based on S1 handover describe how the target eNodeB performsPDCP SN numbering for category-2 packets and category-3 packets so thatthe UE can receive downlink packets sequentially according to PDCP SNand accomplish lossless migration of downlink packets.

The target eNodeB performs PDCP SN numbering for category-2 packets andcategory-3 packets in the following modes:

(1) The target eNodeB performs PDCP SN numbering for category-2 packetsand category-3 packets according to the received message that carriesPDCP SN information of a packet. The following embodiments 1-5 describethis mode.

(2) When the target eNodeB receives a special packet from the sourceeNodeB, the target eNodeB performs PDCP SN numbering for category-3packets by using PDCP SN of the special packet as an initial PDCP SN.The following embodiment 6 describes this mode.

Embodiment 1

In this embodiment, the message that carries the PDCP SN information ofa packet is a Relocation Request message, and the PDCP SN information ofa packet is information about the relationship between the PDCP SN andthe GTP-U SN.

As shown in FIG. 3, after step 2, it is evident that no more downlinkpacket can be sent to the source eNodeB. In this embodiment, when thesource eNodeB decides to send a Relocation Request message, theRelocation Request message carries information about the relationshipbetween the PDCP SN and the GTP-U SN, for example, a specific value ofthe PDCP SN and a specific value of the GTP-U SN of the packet, or thecorresponding relationship between the PDCP SN and the GTP-U SN. If thetarget SGW adds a GTP-U SN into a category-3 packet when delivering thepacket, a PDCP SN can be assigned to each category-3 packet according tothe relationship between the PDCP SN and the GTP-U SN.

The category-2 packet forwarded by the source eNodeB may also carry theold S1 interface GTP-U SN. In this way, it is ensured that the targeteNodeB sequentially receives the packets forwarded by the source eNodeB.The category-2 packet forwarded by the source eNodeB may carry no old S1interface GTP-U SN, and, by default, the target eNodeB believes that thecategory-2 packets forwarded by the source eNodeB arrive sequentially.

For category-2 packets forwarded by the source eNodeB, the target eNodeBmay assign a PDCP SN to each packet according to the order of receivingthe packets. If the category-2 packets forwarded by the source eNodeBcarry old S1 interface GTP-U SNs, the target eNodeB may assign a PDCP SNto each category-2 packet according to the relationship between the PDCPSN and the GTP-U SN.

An exemplary solution to implementing this embodiment is as follows: Itis possible that all the category-1 packets whose PDCP SNs are 1, 2, 3,and 4 in the source eNodeB are sent by the source eNodeB to the UE, butonly the category-1 packets whose PDCP SNs are 1 and 4 are responded to.Therefore, the source eNodeB forwards only the category-1 packets whosePDCP SNs are 2 and 3″ to the target eNodeB. Every packet processedthrough the PDCP carries a PDCP SN, for example, carries category-1packets whose PDCP SNs are 2 and 3; and the packets not processedthrough the PDCP carry no PDCP SN.

It is possible that the source eNodeB carries not only the category-1packets processed through the PDCP, but also the category-2 packets notprocessed through the PDCP. The source eNodeB needs to forward such twotypes of packets to the target eNodeB.

When the source eNodeB decides to send a Relocation Request message, theRelocation Request message carries information about the relationshipbetween the PDCP SN and the GTP-U SN. In this embodiment, theinformation about the relationship between the PDCP SN and the GTP-U SNis the corresponding relationship between the PDCP SN and the GTP-U SN.This corresponding relationship may be calculated out according to thespecific values of the PDCP SNs and the GTP-U SNs in the category-1packets. For example, if a category-1 packet has a PDCP SN being 2 and aGTP-U SN being 10, the corresponding relationship between the PDCP SNand the GTP-U SN may be expressed as “PDCP SN=GTP-U SN-8”. If thecategory-3 packets delivered by the target SGW carry GTP-U SN=15, 16,17, . . . , then the corresponding relationship may be expressed as“PDCP SN=GTP-U SN-8” according to the corresponding relationship betweenthe PDCP SN and the GTP-U SN, and the category-3 packets whose PDCP SNsare 7, 8, 9, . . . .

For the category-2 packets forwarded by the source eNodeB, the targeteNodeB may assign a PDCP SN to each packet according to the order ofreceiving the packets. When the category-2 packets forwarded by thesource eNodeB carry the old S1 interface GTP-U SNs, a PDCP SN may alsobe assigned to each category-2 packet according to the relationshipbetween the PDCP SN and the GTP-U SN. For example, if “GTP-U SN=13, 14”for category-2 packets, the relationship may be expressed as “PDCPSN=GTP-U SN-8” according to the corresponding relationship between thePDCP SN and the GTP-U SN, and the category-3 packets whose PDCP SNs are5 and 6.

In this embodiment, when the source eNodeB decides to send a RelocationRequest message, the Relocation Request message carries the informationabout the relationship between the PDCP SN and the GTP-U SN. In thisway, the category-3 packets from the target SGW can be numbered with thePDCP SNs. The merits of this solution are: The target eNodeB can assigna PDCP SN to each category-3 packet from the target SGW according to therelationship between the PDCP SN and the GTP-U SN, without waiting forcompletion of forwarding all data from the source eNodeB. Therefore, theefficiency of PDCP SN numbering is improved, and the delay of forwardingthe packets is reduced.

Embodiment 2

In this embodiment, the message that carries the PDCP SN information ofa packet is a Handover Confirm message, and the PDCP SN information of apacket is the maximum PDCP SN of the packet received by the UE.

After the UE is synchronized to the target cell successfully, the UEgets in touch with the target eNodeB, as shown in step 11 in FIG. 3. Inthis case, the target eNodeB starts a timer. The UE uses the HandoverConfirm message in step 11 to notify the state of the received packet tothe target eNodeB, including the maximum PDCP SN of the packet receivedby the UE.

The Handover Confirm message sent by the UE to the target eNodeBincludes the maximum PDCP SN of the packet received by the UE.Specifically, the target eNodeB assigns a PDCP SN to each category-2packet and each category-3 packet in this way: If a category-2 orcategory-3 packet carries a GTP-U SN, the target eNodeB assigns a PDCPSN to the packet according to the GTP-U SN of the category-2 orcategory-3 packet. If the category-2 or category-3 packet carries noGTP-U SN, the target eNodeB assigns a PDCP SN to the packet according tothe order of receiving the category-2 or category-3 packet. The targeteNodeB assigns a PDCP SN to each category-2 packet on the basis ofmaximum PDCP SN of the packet received by the UE, and assigns a PDCP SNto each category-3 packet on the basis of the maximum PDCP SN of thecategory-2 packets.

The Handover Confirm message sent by the UE to the target eNodeB carriesthe state information of the packet. The state information may includethe PDCP SN of a non-received category-1 packet. Specifically, thetarget eNodeB sends the category-1 packet to the UE in this way: Thetarget eNodeB forwards the category-1 packets which correspond to thePDCP SNs and are not received by the UE, to the UE, and discards allother category-1 packets.

An exemplary solution to implementing this embodiment is: It is possiblethat all the category-1 packets whose PDCP SNs are 1, 2, 3 and 4 in thesource eNodeB are sent by the source eNodeB to the UE, but only thecategory-1 packets whose PDCP SNs are 1 and 4 are responded to.Therefore, the source eNodeB forwards only the category-1 packets whosePDCP SNs are 2 and 3 to the target eNodeB. Every packet processedthrough the PDCP carries a PDCP SN, for example, carries category-1packets whose PDCP SNs are 2 and 3; and the packets not processedthrough the PDCP carry no PDCP SN.

It is possible that the source eNodeB carries not only the category-1packet processed through the PDCP, but also the category-2 packet notprocessed through the PDCP. The source eNodeB needs to forward such twotypes of packets to the target eNodeB.

When sending a Handover Confirm message to the target eNodeB, the UEnotifies the received packet state information to the target eNodeB. Thestate information may include the maximum PDCP SN of the receivedpackets and the non-received PDCP SNs. For example, the state reportinformation received by the target eNodeB is the maximum PDCP SN=5received by the UE; meanwhile, the target eNodeB receives the PDCP SN=2and PDCP SN=3 of the category-1 packets, and “GTP-U SN=5, 6” of thecategory-2 packets, and the “GTP-U SN=7, 8, 9, . . . ” of the category-3packets forwarded by the target SGW. According to the value of the GTP-USN of the category-2 packets, the category-2 packets whose PDCP SNs are6 and 7 on the basis of the maximum PDCP SN. Afterward, the category-3packets delivered by the SGW whose PDCP SNs are 8, 9, 10, . . . . If thepacket state information sent by the UE further covers the category-1packets that receive no PDCP SN=2, the target eNodeB needs to resend thecategory-1 packets whose PDCP SNs is 2 to the UE, and discard thecategory-1 packets whose PDCP SNs is 3.

In the third, fourth and fifth embodiments, the message that carries thepacket PDCP SN information is: a newly constructed control message sentby the source eNodeB through the source MME and the target MME to thetarget eNodeB; or a newly constructed control message sent by the sourceeNodeB through an X2 interface to the target eNodeB directly.

Embodiment 3

As shown in FIG. 3, after the source eNodeB sends a Handover Command tothe UE after step 10, the source eNodeB knows that the connection withthe UE is interrupted and the data needs to be forwarded. FIG. 4 shows amethod for forwarding downlink packets based on S1 handover in the thirdembodiment of the present disclosure. As shown in FIG. 4, after thesource eNodeB sends a Handover Command to the UE in step 10 and beforethe UE sends a Handover Confirm message to the target eNodeB in step 11,the method further includes: a newly constructed control message is sentby the source eNodeB through the source MME and the target MME to thetarget eNodeB; or a newly constructed control message is sent by thesource eNodeB through an X2 interface to the target eNodeB directly. Thenewly constructed control message carries the initial PDCP SN assignedby the target eNodeB, and the GTP-U SN corresponding to the PDCP SN. Ifthe target SGW adds a GTP-U SN into the category-3 packet whendelivering the packet, the target eNodeB may assign a PDCP SN to eachcategory-3 packet according to the relationship between the PDCP SN andthe GTP-U SN.

By means of an S1 interface, the source eNodeB sends an initial PDCP SNand the GTP-U SN corresponding to the PDCP SN to the target eNodeBthrough the source MME and the target MME, where the initial PDCP SN isthe first PDCP SN assigned by the target eNodeB. The detailed steps areas follows:

Step A1: The source eNodeB sends an initial PDCP SN and the GTP-U SNcorresponding to the PDCP SN to the source MME, where the initial PDCPSN is the first PDCP SN assigned by the target eNodeB.

Step B1: The source MME sends the initial PDCP SN and the GTP-U SNcorresponding to the PDCP SN to the target MME, where the initial PDCPSN is the first PDCP SN assigned by the target eNodeB.

Step C1: The target MME sends the initial PDCP SN and the GTP-U SNcorresponding to the PDCP SN to the target eNodeB, where the initialPDCP SN is the first PDCP SN assigned by the target eNodeB.

Alternatively, the source eNodeB sends an initial PDCP SN and the GTP-USN corresponding to the PDCP SN to the target eNodeB through an X2interface directly, where the initial PDCP SN is the first PDCP SNassigned by the target eNodeB. The detailed steps are as follows:

Step F1: The source eNodeB sends the initial PDCP SN and the GTP-U SNcorresponding to the PDCP SN to the target eNodeB, where the initialPDCP SN is the first PDCP SN assigned by the target eNodeB.

If the target SGW adds a GTP-U SN into the category-3 packet whendelivering the packet, the target eNodeB can assign a PDCP SN to eachcategory-3 packet according to the relationship between the PDCP SN andthe GTP-U SN.

The category-2 packet forwarded by the source eNodeB may also carry theold S1 interface GTP-U SN. In this way, it is ensured that the targeteNodeB sequentially receives the packets forwarded by the source eNodeB.The category-2 packet forwarded by the source eNodeB may carry no old S1interface GTP-U SN, and, by default, the target eNodeB believes that thecategory-2 packets forwarded by the source eNodeB arrive sequentially.

For category-2 packets forwarded by the source eNodeB, the target eNodeBmay assign a PDCP SN to each packet according to the order of receivingthe packets, and the category-2 packets are numbered directly throughthe initial PDCP SN which is the first PDCP SN assigned by the targeteNodeB. If the category-2 packets forwarded by the source eNodeB carryan old S1 interface GTP-U SN, the target eNodeB may assign a PDCP SN toeach category-2 packet according to the relationship between the PDCP SNand the GTP-U SN.

An exemplary solution to implementing this embodiment is: It is possiblethat all the category-1 packets whose PDCP SNs are 1, 2, 3 and 4 in thesource eNodeB are sent by the source eNodeB to the UE, but only thecategory-1 packets whose PDCP SNs are 1 and 4 are responded to.Therefore, the source eNodeB forwards only the category-1 packets whosePDCP SNs are 2 and 3 to the target eNodeB. Every packet processedthrough the PDCP carries a PDCP SN, for example, carries category-1packets whose PDCP SNs are 2 and 3 or category-1 packets forwarded tothe target eNodeB and whose PDCP SNs are 2 and 3; and the packets notprocessed through the PDCP carry no PDCP SN.

It is possible that the source eNodeB carries not only the category-1packet processed through the PDCP, but also the category-2 packet notprocessed through the PDCP. The source eNodeB needs to forward such twotypes of packets to the target eNodeB.

For the category-2 packets forwarded by the source eNodeB, the targeteNodeB may assign a PDCP SN to each packet according to the order ofreceiving the packets, and the PDCP SN value carried in the [A1, B1,C1]/F1 control plane is applied directly. If the category-2 packetsforwarded by the source eNodeB carry the old S1 interface GTP-U SN, thetarget eNodeB may assign a PDCP SN to each category-2 packet accordingto the relationship between the PDCP SN and the GTP-U SN.

In the control plane message in this solution, PDCP SN=5, and GTP-USN=10. The target eNodeB starts numbering from PDCP SN=5. The GTP-U SNsof the packets delivered by the SGW are 12, 13, 14, . . . . Therefore,the target eNodeB numbers the category-3 packets with PDCP SN=7, 8, 9 .. . according to the relationship between the PDCP SN and the GTP-U SNin the control plane message. It is determined that two packets areforwarded from the source eNodeB. The packets which are forwarded fromthe source eNodeB and have no PDCP SN whose PDCP SNs are 5 and 6.

The merits of this solution are: The target eNodeB can number thepackets delivered from the SGW directly, without waiting for completionof forwarding the data from the source eNodeB.

Embodiment 4

As shown in FIG. 3, after the source eNodeB sends a Handover Command tothe UE after step 10, the source eNodeB knows that the connection withthe UE is interrupted and the data needs to be forwarded. FIG. 5 shows amethod for forwarding downlink packets based on S1 handover in thefourth embodiment of the present disclosure. As shown in FIG. 4, afterthe source eNodeB sends a Handover Command to the UE in step 10 andbefore the UE sends a Handover Confirm message to the target eNodeB instep 11, the method further includes: a newly constructed controlmessage is sent by the source eNodeB through the source MME and thetarget MME to the target eNodeB; or a newly constructed control messageis sent by the source eNodeB through an X2 interface to the targeteNodeB directly. The newly constructed control message carries theinitial PDCP SN assigned by the target eNodeB.

The source eNodeB sends the initial PDCP SN through the source MME andthe target MME to the target eNodeB. The detailed steps are as follows:

Step A2: The source eNodeB sends an initial PDCP SN to the source MME.

Step B2: The source MME sends the initial PDCP SN to the target MME.

Step C2: The target MME sends the initial PDCP SN to the target eNodeB.

Alternatively, the source eNodeB sends an initial PDCP SN through an X2interface to the target eNodeB directly. The detailed steps are asfollows:

Step F2: The source eNodeB sends the initial PDCP SN to the targeteNodeB.

The target eNodeB assigns PDCP SNs to the category-2 packets in thefollowing way: The target eNodeB assigns PDCP SNs to the category-2packets according to the initial PDCP SN according to the order ofreceiving the category-2 packets.

After the source eNodeB sends a Relocation Request message to the sourceMME and before the source MME sends a Handover Command to the sourceeNodeB, the following operations may be performed: The source SGW stopssending packets, and the source SGW sends a special packet to the sourceeNodeB. The source eNodeB may forward the special packet, or construct anew special packet and sends it to the target eNodeB. In order to avoidloss of user plane data, one or more special packets may be sent. Forexample, for the GTPU V1 protocol, the information carried in thespecial packet is set through the extended field of the GTP-U packetheader. To construct a special packet in this solution, field 12 orfield 11 in Table 1 may be marked as a special packet, and the specialpacket is set according to Table 3. The field in Table 4 includes a PDCPSN. Table 2 shows the extension of field 12 in Table 1. As shown in FIG.5, the following steps may occur between step 2 and step 3:

Step G1: The source MME instructs the source SGW to stop sendingpackets.

Step H1: The source SGW answers the source MME.

Table 1 shows a GTP-U packet header structure.

TABLE 1 Bits Octets 8 7 6 5 4 3 2 1 1 Version PT (*) E S PN 2 MessageType 3 Length (1st Octet) 4 Length (2nd Octet) 5 Tunnel EndpointIdentifier (1st Octet) 6 Tunnel Endpoint Identifier (2nd Octet) 7 TunnelEndpoint Identifier (3rd Octet) 8 Tunnel Endpoint Identifier (4th Octet)9 Sequence Number (1st Octet)1) 4) 10 Sequence Number (2nd Octet)1) 4)11 N-PDU Number2) 4) 12 Next Extension Header Type3) 4) 1: “version”refers to the version; “PT” refers to the protocol type; “E”: if thevalue is 1, it indicates that the extended field is valid, and, if thevalue is 0, it indicates that no extended field exists; S: if the valueis 1, the serial number in field 9 and field 10 is valid, and, if thevalue is 0, the serial number in field 9 and field 10 is invalid. PN: ifthe value is 1, field 11 is valid, and, if the value is 0, field 11 isinvalid; 2: Message type; 3, 4: Message length; 5, 6, 7, 8: Tunnelidentifier; 9, 10: GTP-U serial number; 11: Serial number; and 12:Extended header type.

Table 2 shows extension of field 12 in Table 1.

TABLE 2 Octets 1 Extension Header Length Octets 2-m Extension HeaderContent Octets m + 1 Next Extension Header Type (note)

TABLE 3 Next Extension Header Field Value Type of Extension Header 00000000 No more extension headers 0000 0001 MBMS support indication 00000010 MS Info Change Reporting support indication 1100 0000 PDCP PDUnumber 1100 0001 Suspend Request 1100 0010 Suspend Response

TABLE 4 Bits Octets 8 7 6 5 4 3 2 1 1 1 2 PDCP PDU number 3 PDCP PDUnumber 4 Next Extension Header Type (note)

It is worthy of attention that the foregoing description is specific tothe GTPU V1 protocol. It is understandable to those skilled in the artthat for the GTPU V2 protocol, a similar field may be applied.

When the target eNodeB receives a special packet forwarded by the sourceeNodeB, the target eNodeB knows that the source eNodeB finishesforwarding data, and begins to number the category-3 packets. The targeteNodeB assigns PDCP SNs to the category-3 packets in the following way:The target eNodeB assigns PDCP SNs to the category-3 packets accordingto the order of receiving the category-3 packets on the basis of themaximum PDCP SN of the category-2 packets.

Alternatives after the source eNodeB sends a Relocation Request messageto the source MME and before the source MME sends a Handover Command tothe source eNodeB, the target eNodeB may start a timer, the timer expirythe numbering of the category-3 packets begins.

An exemplary solution to implementing this embodiment is: It is possiblethat all the category-1 packets whose PDCP SNs are 1, 2, 3 and 4 in thesource eNodeB are sent by the source eNodeB to the UE, but only thecategory-1 packets whose PDCP SNs are 1 and 4 are responded to.Therefore, the source eNodeB forwards only the category-1 packets whosePDCP SNs are 2 and 3 to the target eNodeB. Every packet processedthrough the PDCP carries a PDCP SN, for example, carries category-1packets whose PDCP SNs are 2 and 3; and the packets not processedthrough the PDCP carry no PDCP SN.

It is possible that the source eNodeB carries not only the category-1packet processed through the PDCP, but also the category-2 packet notprocessed through the PDCP. The source eNodeB needs to forward such twotypes of packets to the target eNodeB.

In this embodiment, if the initial PDCP SN in the newly constructedcontrol message is 5, the target eNodeB assigns “PDCP SN=5, 6, . . . ”to the category-2 packets forwarded by the source eNodeB according tothe order of receiving the category-2 packets. When the target eNodeBreceives a special packet, or when the timer expires, it indicates thatthe source eNodeB finishes forwarding the category-2 packets. If thePDCP SN of the category-2 packet at this time is 8, the “PDCP SN=9, 10,. . . ” are assigned to the category-3 packets on the basis of PDCPSN=8.

Embodiment 5

After the source eNodeB sends a Relocation Request message to the sourceMME and before the source MME sends a Handover Command to the sourceeNodeB, the following operation may be performed: The source SGW stopssending packets, and obtains the GTP-U SN of the finally forwardedpacket. FIG. 6 is a flowchart of a method for forwarding downlinkpackets based on S1 handover in the fifth embodiment of the presentdisclosure. The following steps may occur between step 2 and step 3:

Step G2: The source MME instructs the source SGW to stop sendingpackets.

Step H2: The source SGW answers the source MME, and indicates the GTP-USN of the packet finally sent to the source eNodeB. In this case, theRelocation Request message carries the GTP-U SN of the packet finallysent by the source SGW to the source eNodeB. That is, the GTP-U SN ofthe packet initially numbered by the target eNodeB for the category-3packets.

Step 3′: The source MME sends the GTP-U SN to the target MME through aForward Relocation Request message in step 3 in FIG. 3.

Step 5a′: The target MME sends the GTP-U SN to the target MME throughthe Relocation Request message in step 5a in FIG. 3.

As shown in FIG. 3, after the source eNodeB sends a Handover Command tothe UE after step 10, the source eNodeB knows that the connection withthe UE is interrupted and the data needs to be forwarded. As shown inFIG. 6, after the source eNodeB sends a Handover Command to the UE instep 10 and before the UE sends a Handover Confirm message to the targeteNodeB in step 11, the method further includes:

a newly constructed control message is sent by the source eNodeB throughthe source MME and the target MME to the target eNodeB; or

a newly constructed control message is sent by the source eNodeB throughan X2 interface to the target eNodeB directly. The newly constructedcontrol message carries the initial PDCP SN.

The source eNodeB sends the initial PDCP SN through the source MME andthe target MME to the target eNodeB, where the initial PDCP SN is thefirst PDCP SN assigned by the target eNodeB. The detailed steps are asfollows:

Step A3: The source eNodeB sends an initial PDCP SN to the source MME.

Step B3: The source MME sends the initial PDCP SN to the target MME.

Step C3: The target MME sends the initial PDCP SN to the target eNodeB.

Alternatively, the source eNodeB sends an initial PDCP SN through an X2interface to the target eNodeB directly. The detailed steps are asfollows:

Step F3: The source eNodeB sends the initial PDCP SN to the targeteNodeB.

The target eNodeB assigns PDCP SNs to the category-2 packets in thefollowing way: The target eNodeB assigns PDCP SNs that begin from theinitial PDCP SN to the category-2 packets according to the order ofGTP-U SNs of the category-2 packets until the GTP-U SN of the category-2packet is equal to the GTP-U SN-1 received by the target eNodeB in step5a′. According to the order of the GTP-U SN of the category-3 packets,the PDCP SNs are assigned to the category-3 packets on the basis of themaximum PDCP SN of the category-2 packets. Alternatively, when the GTP-USN of the category-3 packet is equal to the GTP-U SN received by thetarget eNodeB in step 5a′, the target eNodeB assigns PDCP SNs to thecategory-3 packets according to the PDCP SN in C3.

An exemplary solution to implementing this embodiment is: It is possiblethat all the category-1 packets whose PDCP SNs are 1, 2, 3 and 4 in thesource eNodeB are sent by the source eNodeB to the UE, but only thecategory-1 packets whose PDCP SNs are 1 and 4 are responded to.Therefore, the source eNodeB forwards only the category-1 packets whosePDCP SNs are 2 and 3 to the target eNodeB. Every packet processedthrough the PDCP carries a PDCP SN, for example, carries category-1packets whose PDCP SNs are 2 and 3; and the packets not processedthrough the PDCP carry no PDCP SN.

It is possible that the source eNodeB carries not only the category-1packet processed through the PDCP, but also the category-2 packet notprocessed through the PDCP. The category-2 packets need to carry theGTP-U SN. The source eNodeB needs to forward such two types of packetsto the target eNodeB.

In this embodiment, if the initial PDCP SN is 5 and the GTP-U SN of thepacket finally forwarded by the source eNodeB is 5, the target eNodeBassigns “PDCP SN=5, 6, . . . ” to the category-2 packets forwarded bythe source eNodeB according to the order of receiving the category-2packets first. When the PDCP SN of the category-2 packet is 7 and theGUP-U SN of the category-2 packet is 5, it indicates that the sourceeNodeB finishes forwarding the category-2 packet, and the target eNodeBassigns “PDCP SN=8, 9, . . . ” to the category-3 packets according tothe order of the GTP-U SN of the category-3 packets on the basis of themaximum PDCP SN of the category-2 packets.

Embodiment 6

The source eNodeB assigns PDCP SNs to all forwarded packets, and makes amark or a special packet for the packet finally sent to the sourceeNodeB to indicate the final packet. In this embodiment, a specialpacket is used to indicate the final packet. At the beginning ofrelocation, the packet in the source eNodeB may include the category-2packets not processed through the PDCP. The source eNodeB uses the PDCPto convert them into the category-1 packets numbered with a PDCP SN, andthen forwards the packets. That is, all the packets forwarded by thesource eNodeB to the target eNodeB are category-1 packets. The packetsreceived by the target eNodeB include the category-1 packets forwardedby the source eNodeB and the category-3 packets delivered by the targetSGW.

After the source eNodeB sends a Relocation Request message to the sourceMME and before the source MME sends a Handover Command to the sourceeNodeB, the following operations may be performed: The source SGW stopssending packets, and affixes a label to the final packet, or makes aspecial packet for the final packet and sends it to the source eNodeB.The source eNodeB may forward the special packet, or construct a newspecial packet and sends it to the target eNodeB. In order to avoid lossof user plane data, the special packet may be sent repeatedly in series.For example, for the GTPU V1 protocol, in order to construct a specialpacket in this solution, field 12 or field 11 in Table 1 may be markedas a special packet, and the special packet is set according to Table 3.The field in Table 4 includes a PDCP SN. It is worthy of attention thatthe foregoing description is specific to the GTPU V1 protocol. It isunderstandable to those skilled in the art that for the GTPU V2protocol, a similar field may be applied.

FIG. 7 is a flowchart of a method for forwarding downlink packets basedon S1 handover in the sixth embodiment of the present disclosure. Thefollowing steps may occur between step 2 and step 3:

Step G3: The source MME instructs the source SGW to stop sendingpackets.

Step H3: The source SGW answers the source MME.

The source eNodeB numbers the received packet with a PDCP SN, and thennumbers the special packet with a PDCP SN.

After receiving the special packet from the source eNodeB, the targeteNodeB knows that the source eNodeB finishes forwarding the packets. Thetarget eNodeB numbers the delivered packets by using PDCP SN of thespecial packet as an initial PDCP SN.

An exemplary solution to implementing this embodiment is: At the time ofrelocation, the source SGW sends three packets and a special packet tothe source eNodeB. The source eNodeB assigns PDCP SNs to the fourpackets with “PDCP SN=1, 2, 3, 4”. After receiving the packets whosePDCP SNs are 1, 2 and 3, the target eNodeB knows that they are forwardedpackets, and send the packets to the UE according to “PDCP SN=1, 2, 3”.After receiving the packet whose PDCP SNs is 4, the target eNodeB knowsthat it is a special packet, and does not send the packet to the UE.According to the special packet, the target eNodeB knows that the sourceeNodeB finishes forwarding the data, and can start numbering the packetdelivered by the target SGW with “PDCP SN=4”.

In the process of forwarding the downlink packets, the target eNodeBneeds to notify the UE of the packet state report information. The UEsends the packet according to the packet state report information. Thefollowing embodiments 7-9 describe a method for forwarding uplinkpackets based on S1 handover.

In the foregoing methods for forwarding downlink packets based on S1handover, the target eNodeB numbers the packets that are received by thetarget eNodeB and carry no PDCP SN according to the received messagethat carries PDCP SN information of the packet, or the newly constructedcontrol message sent by the control plane, or the special packet.Therefore, the UE can receive all packets sequentially in the case of S1handover, and the downlink packets can be forwarded without loss.

Embodiment 7

FIG. 8 is a flowchart of a method for forwarding uplink packets based onS1 handover in the seventh embodiment of the present disclosure. In thisembodiment, the packet state report information includes the PDCP SN ofthe packet finally sent by the source eNodeB. The PDCP SN of the packetfinally and successfully sent by the source eNodeB to the SGW may beconveyed by a newly constructed control message, the newly constructedcontrol message sent by the source eNodeB through the source MME and thetarget MME to the target eNodeB; or a newly constructed control messagesent by the source eNodeB through an X2 interface to the target eNodeBdirectly.

As shown in FIG. 3, after the source eNodeB sends a Handover Command tothe UE after step 10, the source eNodeB knows that the connection withthe UE is interrupted and the data needs to be forwarded. As shown inFIG. 8, after the source eNodeB sends a Handover Command to the UE instep 10 and before the UE sends a Handover Confirm message to the targeteNodeB in step 11, the method further includes: a newly constructedcontrol message is sent by the source eNodeB through the source MME andthe target MME to the target eNodeB; or a newly constructed controlmessage is sent by the source eNodeB through an X2 interface to thetarget eNodeB directly. The newly constructed control message carriesthe PDCP SN of the packet finally sent by the source eNodeB. Meanwhile,the source eNodeB discards the packets which do not arrive sequentially.

Specifically, the source eNodeB sends the target eNodeB the PDCP SN ofthe packet that is finally and successfully sent by the source eNodeB tothe SGW through the source MME and the target MME in the following way:

Step A4: The source eNodeB sends the source MME the PDCP SN of thepacket that is finally and successfully sent by the source eNodeB to theSGW.

Step B4: The source MME sends the target MME the PDCP SN of the packetthat is finally and successfully sent by the source eNodeB to the SGW.

Step C4: The target MME sends the target MME the PDCP SN of the packetthat is finally and successfully sent by the source eNodeB to the SGW.

Alternatively, the source eNodeB directly sends the target eNodeB thePDCP SN that is finally and successfully sent by the source eNodeBthrough an X2 interface to the SGW. The detailed steps are as follows:

Step F4: The source eNodeB sends the target eNodeB the PDCP SN of thepacket that is finally and successfully sent by the source eNodeB to theSGW.

Step E1: The target eNodeB sends the packet state report information tothe UE. The packet state report information carries the maximum PDCP SNof the successfully sent packets, where the maximum PDCP SN is the PDCPSN of the packet finally sent by the source eNodeB to the source SGW.The UE sends the packets subsequent according to this PDCP SN and statereport to the target eNodeB.

An exemplary solution to implementing this embodiment is: In therelocation, the source eNodeB receives the packets whose PDCP SNs are 1,3 and 4, and receives no packet whose PDCP SNs is 2. Therefore, thesource eNodeB sends the packet whose PDCP SNs is 1 to the source SGW.The source eNodeB tells the target eNodeB the maximum PDCP SN=1 sent bythe source eNodeB to the source SGW. Therefore, the target eNodeB tellsthe UE to send the packets whose PDCP SNs are 2, 3, 4 . . . . The UEsends the packets whose PDCP SNs are 2, 3, 4, . . . to the targeteNodeB.

In this solution, the PDCP SN sent by the source eNodeB to the targeteNodeB may be the PDCP SN successfully sent to the source SGW plus 1. Inthe given example, the PDCP SN may be 2. In this case, the target eNodeBknows that the source eNodeB requires the retransmission to start fromPDCP SN=2, and the target eNodeB tells the UE to start sending data from2.

Embodiment 8

FIG. 9 is a flowchart of a method for forwarding uplink packets based onS1 handover in the eighth embodiment of the present disclosure. In thisembodiment, the packet state report information includes: the PDCP SN ofthe special packet sent by the source eNodeB to the target eNodeB.

As shown in FIG. 3, after the source eNodeB sends a Handover Command tothe UE after step 10, the source eNodeB knows that the connection withthe UE is interrupted and the data needs to be forwarded.

After the source eNodeB sends a Relocation Request message to the sourceMME and before the source MME sends a Handover Command to the sourceeNodeB, the following operations may be performed: The source SGW stopssending packets, and starts to send a special packet to the sourceeNodeB. The PDCP SN of the special packet is equal to the PDCP SN of thepacket finally sent by the source eNodeB. Meanwhile, the source eNodeBdiscards the packets that do not arrive sequentially. The source SGWconstructs a special packet and sends it to the source eNodeB. Thesource eNodeB may forward the special packet, or construct a new specialpacket and sends it to the target eNodeB. In order to avoid loss of userplane data, the special packet may be sent repeatedly in series. Forexample, for the GTPU V1 protocol, in order to construct a specialpacket in this solution, field 12 or field 11 in Table 1 may be markedas a special packet, and the special packet is set according to Table 3.The field in Table 4 includes a PDCP SN. It is worthy of attention thatthe foregoing description is specific to the GTPU V1 protocol. It isunderstandable to those skilled in the art that for the GTPU V2protocol, a similar field may be applied.

As shown in FIG. 9, the following steps may occur between step 2 andstep 3:

Step G4: The source MME instructs the source SGW to stop sendingpackets.

Step H4: The source SGW answers the source MME.

Step E2: When the target eNodeB receives the special packet, the targeteNodeB instructs the UE to send the initial PDCP SN of the packet, wherethe initial PDCP SN is the PDCP SN of the special packet.

An exemplary solution to implementing this embodiment is: In therelocation, the source eNodeB receives the packets whose PDCP SNs are 1,3 and 4, and receives no packet whose PDCP SNs is 2. Therefore, thesource eNodeB sends the packet whose PDCP SNs is 1 to the source SGW. Inthis case, the source SGW constructs a special packet and sends it tothe source eNodeB. The source eNodeB sends the special packet to thetarget eNodeB. The PDCP SN of the special packet is set to be the PDCPSN finally sent to the source SGW plus 1. The target eNodeB receives thespecial packet. If the PDCP SN of the special packet is 2, the initialPDCP SN of the packet to be sent by the UE is 2. Therefore, the targeteNodeB tells the UE to send the packets whose PDCP SNs are 2, 3, 4, . .. . The UE sends the packets whose PDCP SNs are 2, 3, 4, . . . to thetarget eNodeB.

In this solution, the PDCP SN of the special packet may also be the PDCPSN successfully sent to the source SGW.

In the given example, the PDCP SN of the special packet may be 1. Thetarget eNodeB and the source eNodeB reach a consensus, and know that theUE needs to start resending data from the PDCP SN+1.

Embodiment 9

FIG. 10 is a flowchart of a method for forwarding uplink packets basedon S1 handover in the ninth embodiment of the present disclosure. Inthis embodiment, the packet state report information includes: the PDCPSNs of the packets not received by the source eNodeB, and the PDCP SN ofthe packets required to be sent sequentially.

As shown in FIG. 3, after the source eNodeB sends a Handover Command tothe UE after step 10, the source eNodeB knows that the connection withthe UE is interrupted and the data needs to be forwarded. As shown inFIG. 10, after the source eNodeB sends a Handover Command to the UE instep 10 and before the UE sends a Handover Confirm message to the targeteNodeB in step 11, the method further includes:

A newly constructed control message is sent by the source eNodeB throughthe source MME and the target MME to the target eNodeB; or

a newly constructed control message is sent by the source eNodeB throughan X2 interface to the target eNodeB directly.

The newly constructed control message carries the PDCP SNs of thepackets not received by the source eNodeB and the initial PDCP SN of thepackets required to be sent sequentially.

The source eNodeB sends the PDCP SN through the source MME and thetarget MME to the target eNodeB. The detailed steps are as follows:

Step A5: The source eNodeB sends the source MME the PDCP SNs of thepackets not received by the source eNodeB and the initial PDCP SN of thepackets required to be sent sequentially.

Step B5: The source MME sends the target MME the PDCP SNs of the packetsnot received by the source eNodeB and the initial PDCP SN of the packetsrequired to be sent sequentially.

Step C5: The target MME sends the target eNodeB the PDCP SNs of thepackets not received by the source eNodeB and the initial PDCP SN of thepackets required to be sent sequentially.

Alternatively, through an X2 interface directly, the source eNodeB sendsthe target eNodeB the PDCP SNs of the packets not received by the sourceeNodeB and the initial PDCP SN of the packets required to be sentsequentially. The detailed steps are as follows:

Step F5: The source eNodeB sends the target eNodeB the PDCP SNs of thepackets not received by the source eNodeB and the initial PDCP SN of thepackets required to be sent sequentially.

Step E3: The target eNodeB sends the packet state report information tothe UE. The UE sends the packets according to the packet state reportinformation. The packet state report information includes: the PDCP SNsof the packets not received by the source eNodeB, and the PDCP SNs ofthe packets required to be sent sequentially.

An exemplary solution to implementing this embodiment is: In therelocation, the source eNodeB receives the uplink packets whose PDCP SNsare 1, 3 and 4, and receives no packet whose PDCP SN is 2. Therefore,the source eNodeB sends the packet whose PDCP SN is 1 to the source SGW,and forwards the packets whose PDCP SNs are 3 and 4 to the targeteNodeB. The source eNodeB tells the target eNodeB that the source eNodeBreceives no packet whose PDCP SN is 2 and tells the target eNodeB tostart sending the packets sequentially from PDCP SN=5. Therefore, thetarget eNodeB tells the UE to resend the packet whose PDCP SN is 2 andsequentially send the packets which start from PDCP SN=5. The UE sendsthe packet whose PDCP SN is 2 to the target eNodeB and sequentiallysends the packets which start from PDCP SN=5. After receiving the packetwhose PDCP SN is 2, the target eNodeB sequentially sends the packetswhose PDCP SNs are 2, 3 and 4 to the SGW, and sequentially sends thepackets whose PDCP SNs are equal to or greater than 5.

In the foregoing method for forwarding uplink packets based on S1handover, the target eNodeB sends the packet state report information tothe UE. Therefore, the UE knows the packets not received by the sourceeNodeB or the PDCP SNs of such packets accurately in the case of S1handover and sends the packets according to the packet state reportinformation, and the uplink packets are forwarded without loss.

In order to implement the method for forwarding downlink packets basedon S1 handover, an eNodeB is disclosed in an embodiment of the presentdisclosure. FIG. 11 shows a structure of an eNodeB in an embodiment ofthe present disclosure. As shown in FIG. 11, when the eNodeB serves as atarget eNodeB, the eNodeB includes:

a receiving module 101, adapted to receive the message that carries PDCPSN information of the packet; and

a sorting module 102, connected with the receiving module 101 andadapted to perform PDCP SN numbering for the packet according to themessage.

In the foregoing embodiment, the message that carries the PDCP SNinformation of a packet is a newly constructed control message sent bythe source eNodeB through the source MME and the target MME. The newlyconstructed control message may include: the initial PDCP SN assigned bythe target eNodeB, and the GTP-U SN corresponding to the initial PDCPSN. Alternatively, the newly constructed control message may includeonly the initial PDCP SN assigned by the target eNodeB to the packet.

In the foregoing embodiment, the message that carries the PDCP SNinformation of a packet is a Relocation Request message sent by thesource eNodeB through the source MME and the target MME. The RelocationRequest message carries the information about the relationship betweenthe PDCP SN and the GTP-U SN.

In the foregoing embodiment, the message that carries the PDCP SNinformation of a packet is a Handover Confirm message sent by the UE.This message carries the maximum PDCP SN of the packet received by theUE.

It is understandable to those skilled in the art that all or part of thesteps of the foregoing embodiments may be implemented by hardwareincluding a processor instructed by a program. The program may be storedin a computer-readable storage medium accessible by the processor. Whenbeing executed, the program instructs the processor to perform thesesteps: numbering a packet not processed by using PDCP according to amessage that carries PDCP SN information if downlink packets to beforwarded include the packet not processed by using PDCP; and sendingthe downlink packets to the UE according to the PDCP SN corresponding tothe packet included in the downlink packets.

Alternatively, the program performs these steps when being executed:numbering a packet not processed by using PDCP according to a messagethat carries PDCP Serial Number (SN) information if downlink packets tobe forwarded include the packet not processed by using PDCP; and sendingthe downlink packets to the UE according to the PDCP SN corresponding tothe packet included in the downlink packets. Alternatively, the programperforms these steps when being executed: receiving state reportinformation of the packet sent by the target eNodeB; and sending thepacket according to the state report information of the packet.

The storage medium may be a magnetic disk, compact disk, Read-OnlyMemory (ROM), Random Access Memory (RAM), and so on.

Although the disclosure is described through some exemplary embodiments,the disclosure is not limited to such embodiments. It is apparent thatthose skilled in the art can make modifications and variations to thedisclosure without departing from the spirit and scope of thedisclosure. The disclosure is intended to cover the modifications andvariations provided that they fall in the scope of protection defined bythe following claims or their equivalents.

What is claimed is:
 1. A method for forwarding downlink packets,comprising: receiving, by a target evolved NodeB (eNodeB), when ensuringa lossless handover for a user equipment (UE), a control message outsidea user plane from a source eNodeB, the control message including aninitial Packet Data Convergence Protocol (PDCP) serial number (SN) and adefined relationship between the initial PDCP SN and a GPRS tunnelingprotocol user serial number (GTP-U SN); receiving, by the target eNodeB, a plurality of packets without processing (non-PDCP packets), eachnon-PDCP packet in the plurality of non-PDCP packets being alreadynumbered with its corresponding unique GTP-U SN; processing, by thetarget eNodeB, the plurality of non-PDCP packets into PDCP packets byassigning the initial PDCP SN for a first non-PDCP packet, and assigninga PDCP SN to each remaining non-PDCP packet in accordance with the GTP-USN corresponding to the remaining non-PDCP packet and the relationshipbetween the initial PDCP SN and the GTP-U SN of the first non-PDCPpacket; and sending, by the target eNodeB, the PDCP packets to the UE.2. The method according to claim 1, further comprising: receiving, bythe target eNodeB, the plurality of non-PDCP packets from the sourceeNodeB.
 3. The method according to claim 1, wherein the control messageis sent from the source eNodeB to the target eNodeB through a mobilitymanagement entity (MME).
 4. The method according to claim 3, wherein thecontrol message is sent from the source eNodeB to the target eNodeBthrough a MME further comprising: the control message is sent from thesource eNodeB to the target eNodeB through a source MME and a targetMME.
 5. An evolved NodeB (eNodeB), comprising: a receiving unit,configured to receive, when ensuring a lossless handover for a userequipment (UE), a control message outside a user plane from a sourceeNodeB, wherein the control message includes an initial packet dataconvergence protocol serial number (PDCP SN) and a defined relationshipbetween the initial PDCP SN and a GPRS tunneling protocol user serialnumber (GTP-U SN), and wherein the receiving unit is further configuredto receive a plurality of packets without processing (non-PDCP packets),each non-PDCP packet in the plurality of non-PDCP packets being alreadynumbered with its corresponding unique GTP-U SN; a sorting unit,connected with the receiving unit and configured to perform processingthe plurality of non-PDCP packets into PDCP packets by assigning theinitial PDCP SN for a first non-PDCP packet, and assigning a PDCP SN foreach remaining non-PDCP packet in accordance with the GTP-U SNcorresponding to the remaining non-PDCP packet and the relationshipbetween the initial PDCP SN and the GTP-U SN of the first non-PDCPpacket; and a sending unit, configured to send the PDCP packets to theUE.
 6. The eNodeB according to claim 5, wherein the receiving unit isfurther configured to receive the plurality of non-PDCP packets from thesource eNodeB.
 7. The eNodeB according to claim 5, wherein the receivingunit is further configured to receive the control message through amobility management entity (MME).
 8. The eNodeB according to claim 7,wherein the receiving unit is further configured to receive the controlmessage through a source MME and a target MME.